Modest elevations in cancer rates post-exposure to the World Trade Center (WTC) disaster site have now been reported in all three cohorts of rescue/recovery workers, despite limited follow-up time since 9/11/2001. The first major WTC cancer incidence study was carried out by our research group and served as the impetus for adding cancer to the list of health conditions covered by the James Zadroga 9/11 Health and Compensation Act of 2010, under the auspices of the National Institute for Occupational Safety and Health (NIOSH). NIOSH has sponsored meetings to discuss assessment of the possible association of WTC exposure with cancer. One important conclusion from those meetings was the realization that WTC-exposed cohorts lack appropriate comparison populations; another was that it is difficult to accurately characterize exposure to the WTC site. The overarching goal of our current proposal is to address these problems and thereby further our understanding of the association between WTC exposure and cancer risk. Results from a NIOSH study of non- WTC-exposed firefighters were recently published and its investigators have agreed to collaborate with us as part of the current proposal. This collaboration will, for the first time, provide an ideal comparison population for WTC-exposed firefighters from the Fire Department of the City of New York (FDNY) cohort, allowing us to differentiate between excess cancers potentially attributable to firefighting exposures from excess cancers potentially attributable to work at the WTC site. In addition, we propose to use FDNY work records to better estimate the duration of WTC work exposure during the 10-month rescue/recovery period, creating an exposure metric that is independent of recall bias. Finally, we will use new information generated by this proposal to project the range of expected new cancer cases among WTC-exposed firefighters through 2035 to facilitate long-term planning. The specific aims of this proposal are: Aim 1) Compare cancer incidence rates in FDNY WTC-exposed firefighters to rates in non-WTC-exposed firefighters; Aim 2) Develop a new measure of duration of WTC exposure based on FDNY work assignment records and model cancer incidence rates as a function of first arrival time to the WTC site and the new duration measure; and Aim 3) Estimate the future burden of cancer in WTC-exposed firefighters to facilitate planning and policy decisions.